Question

A well known antibiotic penicillin , contains C 57. 49,H 5.39,N 8.395, S 9.58 ,the reminder being oxygen given that penicillin contains one atom of sulphur molecule,calculate the molecule formula of the antibiotic.

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Answer 1

Given:

Percentage of  elements present in penicillin

C = 57.49%

H =5.39%

S = 9.58%

N = 8.395%

O = remaining

1 atom of sulphur present in molecular formula

To Find:

The molecular formula of antibiotic

Solution:

Now, we can find the molecular formula by following method,

$\begin{center}\begin{tabular}{ c c c } Element & Percent & Atomic mass \\ C & 57.49 & 12 \\ H & 5.39 & 1 \\ N & 8.395 & 14 \\ S & 9.58 & 32 \\ O & 19.145 & 16 \\\end{tabular}\end{center}$

here, the relative number of atoms can be calculated as

$=\dfrac{percentage}{atomic mass}$

$\begin{center}\begin{tabular}{ c c c } Relative no. of atoms & Simplest atomic no. & simplest whole no. ratio \\ C- 57.49/12 = 4.79 & 4.79/0.29 = 16.51 & 16 \\ H = 5.39 & 18.58 & 18 \\ N = 0.59 & 2.03 & 2 \\ S = 0.29 & 1 & 1 \\ O = 1.19 & 4.10 & 4 \\\end{tabular}\end{center}$

by using the simplest whole no. the ratio also the given information that penicillin contains 1 sulphur molecule

the molecular formula of antibiotic is  $C_{16}H_{18}N_{2}SO_{4}$